Coil bobbin



G. L. OSBORNE I COIL BOBBIN Filed April 20, 1948 June 13, 1950 INVENTOR.ird/0 L. [7560mm Patented June 13, 1950 UNITED STATES PATENT OFFICE 6Claims.

This invention relates to a. coil bobbin, spool or the like.

It is an object of the present invention to provide a new bobbinconstruction having improved electrical insulation characteristics.

A further object of the present invention is to provide a compact,simple and inexpensive bobbin construction such as for transformer coilsand which provides improved insulation between the coil turns and theiron core element.

More specifically, it is an object of the present invention to provide anew and improved flange structure for coil bobbins for transformers andthe like electrical devices and which may be readily manufactured andassembled with a minimum of effort and without requiring expensivetools.

In accordance with an illustrated embodiment, the coil bobbin of theinvention comprises :a core having end flanges mounted thereon andsecured thereto by means of tab portions integral with the flanges andwhich are imbedded between superimposed turns of the core element, theend flanges being of rectangular shape and of flexible insulatingmaterial providing outer flap portions adapted to be folded over theperipheral outer surface of the coil and providing long creepage pathsbetween the outer turns of the coil and the adjacent iron corestructure.

For a consideration of what is believed novel and inventive, attentionis directed to the following description taken in conjunction with theaccompanying drawing while the features of novelty will be pointed outwith greater particularity in the appended claims.

In the drawings, Fig. 1 is a view in perspective illustrating atransformer incorporating a coil unit wound on a bobbin constructed inaccordance with one form of the present invention, a portion of theinsulation covering being removed to illustrate certain details; Fig. 2is a view in perspective illustrating a partially completed bobbinconstructed in accordance with one form of the present invention; Fig. 3is a longitudinal sectional view taken through a partially completedcoil unit; Fig. 4 is a plan view illustrating one of the flange elementsincorporated in the bobbin; Fig. 5 is an exploded view illustrating onemanner in which the bobbin elements may be assembled; Fig, 6 is a viewin perspective illustrating a transformer including a bobbin unitconstructed in accordance with a second modification of the invention, aportion of the insulation covering for the bobbin unit being broken awayso as more clearly to illustrate certain details of construction; Fig. 7is a side elevation of a bobbin incorporated in the transformer shown inFig. 6, a portion of the bobbin being removed for more clearlyillustrating certain details of construction; and Fig. 8 is a plan viewillustrating a flange unit incorporated in the bobbin shown in Fig. 7.

Referring now to the drawings, in Fig. 1 is shown a transformercomprising a laminated core unit It] having a coil unit Ii arranged uponthe central leg 12 thereof. The coil unit it is wound upon a bobbinconstructed in accordance with one form of the present invention andwhich is so designed as to be capable of inexpensive manufacture and atthe same time provide high insulation strength between the coil turnsand the iron core l0.

Referring now particularly to Figs. 2, 3, and 4, the coil bobbinconsists of a rectangular core 14 having generally rectangular flanges I5 mounted on each of the opposite ends thereof. While in the drawings,the corners are shown as being square, these may be rounded if desired.Preferably, though not necessarily, the core 14 consists of a pluralityof turns of flexible insulating material, such as paper, suitablycemented together. The end flanges 15 are also made of a relativelyflexible insulating material, such as paper, one of which is illustratedmore clearly in the plan view of Fig. 4.

The flanges I5 are each provided with a central rectangular openingindicated by the dotted fold lines 16 corresponding to the outerdimensions of the core element 14. Tabs 11 are formed by slittingthrough the material along the crossed lines indicated at 18 and'the tabportions are bent outwardly along the fold lines It to a position atright angles with respect to the plane of the remainder of the flange15. Each of the triangular tab portions 11 is, of course, integral withthe flange 15 throughout the full extent of the edge portions thereofdefining the opening therethrough. Particular attention is directed tothe fact that the edges of the opening through the flange l5 extend at a45 degree angle with respect to the outermost edges of the flange andwhich is important for reasons which will be described more fullyhereinafter. While in the drawings, the tabs 11 are shown as beingtriangular in shape, it is understood that the tips may be cut off inthe manufacture of short bobbins.

As illustrated in Fig. 2, the flanges 15 are assembled upon the oppositeends of the core element 14 with the triangular tab portions 11 of theflanges extending toward each other and positioned upon the outersurfaces of the core element. The flanges l5 may be secured in positionupon the core element in any suitable manner, such as by a number ofadditional turns of insulating material wr'apped about the core 14 andover the upper surfaces of the triangular tab portions 11. Theseadditional turns are indicated in Fig. 3 at 20.

The coil may then be wound about the bobbin in accordance with customarypractice, the low voltage turns being provided next adjacent the coreelement 14 of the bobbin and the high voltage turns wound thereabout. Asillustrated, the coil winding 2| consists of a multiplicity of turns ofsuitably insulated conductor with no interlayer insulation. After arequisite number of turns have been provided upon the bobbin, a layer 22of insulation may be wrapped about the coil and the corner portions ofthe flanges, indicated at 23, are then folded tightly thereagainst andfurther secured in place by one or more turns of insulating material 24wrapped thereabout. The entire coil unit may then be treated in theusual manner such as by immersion in an insulating varnish orother'resinous insulating material and baked.

As illustrated more clearly in the view of Fig. 1, in which a portion ofthe outer wrapping 24 of insulation has been removed from the peripheryof the winding unit, it will be observed that the ends of the windingcoil are completely covered with a continuous layer of insulatingmaterial between the winding and the outer corners 26 of the iron corestructure Hi. It will be observed that the outer corner portions 23 ofthe flange elements extend from each of the opposite sides of the ironcore structure 58, at the outer corner edges of the winding by aconsiderable distance indicated at 27. In other words the maximum widthof the folded corner portions 23 is considerably greater than the widthof the iron core. A long leakage path is thus provided between the ironcore H3 and the winding turns around the edges of the flange elements 15of the bobbin and which, accordingly, provides a high value ofinsulation between the iron core and the winding,

1' am well aware of the fact that it has been long recognized in the artthat it is necessary to provide adequate insulation between the cornersof the winding unit and the adjacent corner portions of the iron core,indicated at 26, and which points are recognized as the points of greatelectrical weakness in a transformer structure. Ihave discovered thatwith the coil bobbin structure of the present invention, I have beenable to provide adequate insulation strength between the winding andthecore structure and at the same time achieve a greatly improved spacefactor between the coil unit and the iron core structure so that theover-all dimensions of the transformer are reduced substantially ascompared with other prior art devices of similar capacity. Thisreductionin overall size of the transformer unit is of vital importance in manyapplications where space is at a premium. Moreover, with the bobbin andinsulation arrangement as disclosed, the overall manufacturing cost ofthe transformer unit is reduced very substantially as compared withusual costs for transformers of the type described.

Referring now to Fig. 5 a modification of the invention will bedescribed and in which the core unit 14 is formed by wrapping arelatively few turns 30 about a mandril, following which the end flangesl5 as previously described may be assembled upon the opposite ends ofthe partially formed core element. It will be observed that the unwoundportion 3| of the web of insulating material will extend through thecorners between adjacent pairs of triangular tabs of the end flanges soas to permit assembly of the flange units [5 upon the open ends of thepartially formed core element. The remaining turns of the web 3! maythen be wound upon the core unit over the triangular tab portions 5'! aspreviously described securely anchoring the flanges 15 in place.

Referring again to the view of Fig. 1, it will be observed that thethickness of the winding coil 2| corresponds substantially to thedistance between the corners of the openings in the end flanges and theadjacent outer edges of the flanges, which distance is indicated at 35in Fig. 4. The reason for this is to facilitate the folding over of theouter corner portions 23 of the flanges without causing buckling of theflange portions at the corners 35 of the coil as indicated in Fig. 1. Inthe modification illustrated in Figs. 6, '7 and 8 the end flanges All ofthe bobbin are formed of a semi-elastic flexible insulating material.While various suitable materials are available upon the market, I preferto use a resinous thermo-plastic insulating material. By using such amaterial the creepage paths around the end; flanges of the bobbin may beconsiderably increased. As illustrated in Fig. 8, the triangular tabportions 33- are formed by cross slitting along the lines 4|. The crossslits 4| are somewhat shorter than the diagonals of the ultimate openingto be formed therein and indicated by the fold lines 12. In Fig. 7 theflanges 3% are shown mounted upon a core element 44 with the triangulartab portions 43 extending at right angles with respect to the plane ofthe flange do and positioned against the opposite sides of the coreelement 44. The corner portions integral with each of the adjacent tabs43 are formed by stretching the plastic material suiflciently to permitmounting of the flanges upon the core. The corner portions 45 thusformed increase very substantially the leakage path between the centralleg of the iron core and the innermost turns of the winding coil.

As illustrated in Fig. 6 the flanges it are in this instance somewhatlarger than the previously described flanges l5, as compared with thedimensions of the winding coil, and particularly as regards the distancebetween the corners of the inner opening and the outer edge indicated at41 in Fig. 8. Due tothe plastic nature of the insulatingmaterial, theportions 48 of the flange between the corner portions 49 may be foldedsmoothly over the corners of the coil to permit the outer insulationwrapping layer 5i to lie smooth thereabout. By virtue of the fact thatthe portions 48 of end flanges extend over the corners of the windingcoils as shown in Fig. 6 a substantial increase in creepage pathdistance is accomplished as compared with the modification of Fig. 1.

Having described and illustrated what is considered to be certainpreferred embodiments thereof it is desired that it be understood thatthe present details shown are merely representative and that theinvention may be carried out by other means.

I claim:

1. A coil bobbin, of the class described compris- 76 ing a core ofrectangular cross section, flanges mounted on the opposite ends of saidcore, each of said flanges being of flexible insulating material and ofrectangular shape, a centrally disposed rectangular opening in each ofsaid flanges, the edges of said openings extending at a 45 degree anglewith respect to the outer edges of said flanges, triangular tabsextending at right angles from the inner faces of each of said flangesand integral with each of the opposite edge portions defining saidopenings throughout the full extent thereof, a plurality of turns ofinsulating material covering said tabs and securing said flanges to saidcore, the outer corners of said flanges being adapted to be folded overthe outer peripheral surface of a coil wound about said core betweensaid flanges.

2. A coil bobbin of the class described comprising a core of rectangularcross section, flanges mounted on the opposite ends of said core, eachof said flanges being of flexible insulating material and of rectangularshape, a centrally disposed rectangular opening in each of said flanges,the edges of said openings extending at a 45 degree angle with respectto the outer edges of said flanges, triangular tabs extending at rightangles from the inner faces of each of said flanges and integral witheach of the edge portions defining said openings throughout the fullextent thereof, a plurality of turns of insulating material coveringsaid tabs and securing said flanges to said core, a coil wound aboutsaid core, the width of said flanges between the corners of saidopenings and the adjacent outer edges of said flanges being at leastequal to the thickness of said coil, the outer corner portions of saidflanges being folded over the outer peripheral surface of said coil andextending parallel with the axis of said core.

3. A coil bobbin of the class described comprising a core of rectangularcross section, flanges mounted on the opposite ends of said core, eachof said flanges being of flexible insulating material and of rectangularshape, the central portion of each of said flanges defining fourtriangular tabs, said tabs extending at right angles from the innerfaces of said flanges, the fold lines of said tabs extending at a 45degree angle with respect to the outer edges of said flanges, aplurality of turns of insulating material covering said tabs andsecuring said flanges to said core, the outer corners of said flangesbeing adapted to be folded over the outer peripheral surface of a coilwound about said core between said flanges, the width of said foldedcorner portions being greater than the width of said core.

4. A coil bobbin of the class described comprising a core of rectangularcross section adapted to have a coil wound thereabout, rectangularflanges mounted on the opposite ends of said core, the outer edges ofsaid flanges extending at a substantially 45 degree angle with respectto the ad- Jacent flat sides of said core, each of said flanges being offlexible insulating material and having opposite corner portionsextending outwardly from said core substantially beyond the outer edgesof the coil wound upon said core, the outer corners of said flangesbeing adapted to be folded over the outer peripheral surface of the coilwound about said core between said flanges, the width of the fold linesof said corner portions being substantially greater than the width ofsaid core.

5. A coil bobbin of the class described comprising a core of rectangularcross section adapted to have a coil wound thereabout, flanges mountedon the opposite ends of said core, each of said flanges being offlexible insulating material and of rectang111ar shape, the outer edgesof said flanges extending at a substantially 45 degree angle withrespect to the adjacent flat sides of said core, the central portion ofeach of said flanges being slit so as to define a plurality of tabs,said tabs extending at right angles from the inner faces of said flangesand secured to the outer surface of said core, the width of said flangesfrom the tips of the outer corner portions to said core being greaterthan the width of the coil wound on said core, the outer portions ofsaid flanges being adapted to be folded over the outer peripheralsurface of a coil wound about said core between said flanges.

6. A coil bobbin of the class described comprising a tubular core ofrectangular cross-section, flanges mounted on the opposite ends of saidcore, each of said flanges being of flexible insulating material and ofgenerally rectangular shape, the outer edges of said flanges extendingat a substantially 45 degree angle with respect to the adjacent flatsides of said core, a coil wound about said core between said flanges,the minimum width of said flanges between the corners thereof and saidcore being at least equal to the thickness of said coil, the width ofsaid flanges from the tips of the outer comer portions thereof to saidcore being substantially greater than the thickness of said coil, saidcorner portions being adapted to be folded over the outer peripheralsurface of said coil and extending parallel with the axis of said core.

GERALD L. OSBORNE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,481,190 Durbin et a1 Jan. 15,1924 1,859,248 Strait May 1'7, 1932 1,997,641 Isenberg Apr. 16, 1935FOREIGN PATENTS Number Country Date 4,306 Great Britain Oct. 22, 1880

